Agronomists in maximizing the potential of

Transcription

1 Science The role of Agronomists in maximizing the potential of biotech traits by Madeline Fisher 4 CSA News June 2011

2 Fred Below already thinks corn is pretty perfect. Just look at its innate versatility and responsiveness to management, says the ASA and CSSA member, and it s easy to see why it s our highestyielding crop. But even perfection can be improved upon sometimes, and today genes from other organisms are giving corn a boost. Since 1996, when genetically modified hybrids that kill the European corn borer by producing toxins from the Bt bacterium were introduced, the ensuing bump in yield has brought an estimated $7 billion to farmers in five states, according to a 2010 report in Science. Below, a plant physiologist at the University of Illinois in Urbana Champaign, is even more excited about the Bt rootworm trait, which combats rootworm in a similar way. Not only is the pest the most damaging one in his state, he says, but the benefits of healthier, longer-acting roots in corn could be vast. To my mind, it s sort of the game-changer, Below says, because all of a sudden, almost all the investment that the plant made in the root system is protected. Even though Below recognizes the power of biotech traits, he is among a growing group of researchers who believe we re putting too many hopes and too much emphasis on biotechnology today. A look at the trend in federal research dollars says it all: Funding for fields like genomics and molecular genetics has skyrocketed in recent years, while money for applied, agricultural research has stagnated. Some government officials and seed companies have also made predictions that echo those funding trends, much to the dismay of agronomists. In one oft-quoted 2009 research report in the journal Plant Physiology, for example, the authors estimate that biotechnology and molecular marker-assisted breeding will make greater and greater contributions to corn yield over the next 20 years from roughly 1 ton/ acre now to nearly 10 times that by Meanwhile, they predict that agronomy s impact will remain flat at just under 5 tons/acre, or 25% of the total yield by Others (agronomists, not surprisingly) put agronomy s contribution to yield gains closer to 50%. But arguing percentages isn t really the point, Below says. It doesn t matter if you have better biotech traits if you don t take advantage of them and know how to manage them. That s where the void is, really. There s a huge void there. June 2011 CSA News 5

3 Science Photo courtesy of the University of Arkansas Division of Agriculture. A More Balanced, Integrated Approach to Enhance Yields He and others around the country are now calling for a return to a more balanced and integrated approach to enhancing crop yields in the coming years one that brings to bear all the ingenuity and technology we can muster, including conventional breeding, novel tillage systems, innovative machinery, advanced agronomic knowledge, and, yes, biotechnology. After all, this is how scientists achieved the first Green Revolution and the tremendous yield gains of the past 50 years: by deploying a whole series of innovations, including better genetics, irrigation, nitrogen fertilizer, integrated pest management, highprecision planters the list goes on and on. There is no magic bullet, says ASA and SSSA Fellow Paul Fixen of the International Plant Nutrition Institute. I don t care if you re talking about genetics, or plant protection products, or anything else. There is no single solution to the challenge that agriculture is facing to an increasing extent as we look to the future. Most scientists agree that the challenge of the future is immense. The global population is predicted to plateau at around 9 billion people by 2050 a staggering number considering that one in seven people today are already hungry, according to the United Nations Food and Agriculture Organization. At the same time, urban development and industrialization are expected to consume more than 100 million hectares of arable land an area roughly three times greater than the current corn acreage in the United States. And we can forget about expanding agriculture onto new lands, says ASA, CSSA, and SSSA Fellow Ken Cassman, an agronomist at the University of Nebraska Lincoln. Most of those left today are either marginal for agriculture, meaning they lose nutrients and soil when farmed for high yields, or they re carbon-rich ecosystems, such as rainforests or savanna, which release huge amounts of greenhouse gases when plowed. Add it all up, Cassman says, and the bottom line is that average crop yields will need to increase exponentially by 1.3 to 1.4% per year over the next 40 years, while production is held to existing farmlands. Annual increases of this magnitude may not seem like much, and in fact, global maize yields are growing at about this rate. But rather than being exponential, past yield gains in corn and other crops have been linear, meaning that the relative rate of gain declines over time as average yields rise, Cassman explains. From 1961 to 1990, for example, yields per hectare of soybeans, rice, and maize grew annually at rates of 2%, while rates for wheat were as high as 3%. Since 1990, though, those rates have dropped below 1% for all crops except corn. The point is that current rates of gain are already below the rate of gain we re going to need if we re going to hold agriculture to existing arable land, he says. The numbers are sobering enough, but Cassman has also seen the challenges firsthand. In addition to working on all the major crops in the United States, he studied rice production throughout Asia for the International Rice Research Institute during the 1990s. He also witnessed the conversion of virgin rainforest to cropland while stationed for a time in the Amazon Basin. Through those experiences, he says that two things became very clear. For one, the amount of land that can support highyield agriculture is much smaller than we think, especially if we also hope to protect carbon-rich areas like rainforests. And second, it s very hard to grow high-yield crops consistently, he says. Very, very hard. 6 CSA News June 2011

4 What makes the task so difficult is that yield is never determined simply by genetics or any other single factor, although we seem to be forgetting this in our excitement over biotechnology and genomics, says ASA Fellow and Purdue University agronomist Tony Vyn. Instead, yield always emerges from complex interactions among crop genotype, the way that genotype is managed in the field, and the myriad and unpredictable environmental conditions that can limit production, including rainfall, pests, and nutrients. Enter the agronomist, whose job is to understand and balance all those factors. Ultimately, I think the agronomist has to be the integrator, Vyn says, who deciphers the management approach that best resolves the specific abiotic and biotic stress factors that limit yield for a given genotype in a specific production environment. Without that management expertise, new cultivars are like race cars equipped with powerful and highly efficient engines, but which never reach top speed because they aren t taken out on the open road, says ASA and CSSA Fellow Brett Carver, an Oklahoma State University wheat breeder. A new variety that s capable of yielding 60 bu/ac, for instance, will never reach that potential if farmers continue to grow it in a 30 bu/ac environment. You re never going to see that race car go faster if you force it to drive 25 miles per hour, Carver says. High-Tech Management for High-Tech Traits Moreover, the main factor that puts the brakes on yield shifts constantly, adds Below. It s the law of the minimum: Identifying and removing one critical limiting factor, such as disease, can allow farmers to take a step forward in yield until they bump Ultimately, I think the agronomist has to be the integrator who deciphers the management approach that best resolves the specific abiotic and biotic stress factors that limit yield for a given genotype in a specific production environment. up against the next limitation, say lack of a micronutrient. This traditional approach to raising yield works fine in general, Below says; however, when the goal is to reach a whole new yield level, it s not enough. Now, we need to manage a bunch of things together, he says, which is precisely the idea behind the high-technology package of five optimized management practices and inputs that he and his collaborators recently put together. The package is expressly designed to exploit new biotech traits in corn; specifically, so-called triple-stack or smart-stack genetically engineered hybrids that simultaneously tolerate Roundup and fight corn borer and rootworm. But true to his systems philosophy, Below combined the hybrids with four high-tech agronomic practices that are known individually to enhance yield, such as planting corn at high densities and applying a foliar fungicide at flowering to control leaf disease and relieve plant stress. In 2009 and 2010, his research team then examined the ability of the entire Photo by Stephen Ausmus (USDA-ARS). June 2011 CSA News 7

5 Science not the case in most of Vyn s experiments). But protecting yield in this way is not the same as pushing yield, Below says. For that, you need an integrated, agronomic approach. Yes, you ll get more yield with that trait alone it you re losing yield due to the insect, he says, but you ll not get more yield than you would have in the absence of the insect, unless you manage the trait. Photo courtesy of USDA-ARS. package to increase yields across multiple sites in Illinois compared with a traditional management system that contained none of the high-tech components. To further understand how each individual factor contributed to yield, they also employed an omission plot design, in which they added each practice one by one to the traditional system or subtracted them one at a time from the high-tech system. They found that while the relative importance of each factor varied across years and sites, the value of a single component was always greater when combined with the others in the full package than it was on its own. Although the results have yet to be published, they support Below s hypothesis that no single tool, no matter how powerful, will get us where we want to go and that includes biotech. Rather it s the synergies now of better genetics, better fertilizers, and protection chemicals like fungicides, he says. All of those things multiply together. In studies of the effects of plant population number and nitrogen rate on corn yields and nitrogen use efficiency, Vyn too, has found that the Bt rootworm trait cannot by itself alleviate the added nitrogen stress that corn plants experience when crowded together at high densities. That s not to say the trait has no value, he cautions. However, the results do suggest there is no inherent yield advantage associated with Bt rootworm resistance, he says, that renders the genotype suddenly more able to take up nutrients, for example. Farmers may see yields climb with the trait, however, if they re growing crops in areas where rootworm pressure is high (something that was Intelligent Intensification If we do learn to manage biotech traits properly, Below is fully confident that we can push corn yields above ambitious targets, such as 300 bu/ac the much talked about goal that growers are aiming for by And, in fact, entrants in the National Corn Growers Association s annual corn yield contest are already hitting that mark. But reaching those levels today also requires a no-holds-barred, throw-every-input-at-it approach. The trick in the future will be to hit these targets without degrading the planet with more fertilizers, pesticides, erosion, and greenhouse gas emissions. Now it s about intelligent intensification, Below says. Using the inputs in the right way and the right place. Fortunately many researchers are already studying the impacts of agriculture on the environment with an eye toward reducing farming s footprint, just as many others are working on ways to increase productivity. The problem is that the two groups aren t working together to achieve both goals at the same time, Cassman says. Thus, for more than a decade he has been calling for a strategy of ecological intensification that unites many disciplines including plant physiology, agroecology, and soil science in achieving consistently high yield levels while simultaneously working toward long-term agricultural sustainability. For example, Vyn says, future studies of corn hybrids that possess drought tolerance traits ideally will involve a range of scientists, in- 8 CSA News June 2011

6 cluding crop physiologists who study plant stress tolerance in the context of interacting factors, such as plant density; meteorologists who look at transpiration and water use efficiency; and soil scientists who examine carbon sequestration and trace gas emissions in rain-fed systems where yield is being optimized with nutrients. Fixen, for his part, calls this a systems approach one that considers all of the interacting aspects of agricultural ecosystems and doesn t get too hung up on the magic bullets, such as genomics or biotech. It s a matter of looking at all of the resources at our disposal, which are connected to agriculture s ability to do what society wants us to do, he says, and then optimizing the whole package. We still need specialists, don t get me wrong. But we also need people who can put all the parts together to simultaneously accomplish production and environmental objectives. accomplish production and environmental objectives. But achieving broad training of students requires money for this type of research, of course. And while Fixen sees the USDA Agriculture and Food Research Initiative s (AFRI s) support of large, regional, interdisciplinary projects as a big step in the right direction, more funding is desperately needed. That s why at an even more fundamental level, we must set the proper goal, Cassman says. The past 30 years of abundant food have given us the luxury of chasing scientific questions that, although interesting and important, are likely never to bring to us the same agricultural bounty in the future. So it s time now to ask for a shift in scientific priorities: specifically toward those that will achieve a 70% increase in yields on existing farmlands while also dramatically reducing agriculture s negative environmental impacts. If everyone demanded this kind of research along with evidence that it was producing results, I guarantee you, we would see a different research agenda, Cassman says. There would still be some research on transgenic plants and genomics we need those tools, there s no question. It would just be a smaller portion. M. Fisher, CSA News magazine lead writer; mfisher@sciencesocieties.org What Will It Take to Get There? The remaining question is what will it take to get there? First and foremost, the scientists agree that we should not only be producing many more agronomic scientists overall, but more critically, researchers who are broadly trained to handle the complexities of modern day agricultural problems and find integrated solutions. Driven by trends in funding, agricultural students today often focus instead on narrow objectives, Fixen says, such as measuring greenhouse gas emissions. It s a development that worries him. We still need specialists, don t get me wrong, he says. But we also need people who can put all the parts together to simultaneously Photo on originally submitted with a Crop Science article by Norman Taylor (2008; 48:1-13). June 2011 CSA News 9